The invention applies especially to counting the axles of vehicles on a road. Axle-counting devices are known which are constituted by pneumatic or electric sensors disposed across the surface of a roadway. However, such sensors disposed directly on the roadway may suffer damage or may be torn away, in particular in snowbound regions when snow-ploughs pass over them. Piezo-electric sensors have then been used, disposed in roadways but whereas operation is satisfactory in the case of asphalt roadways, it is not in the case of concrete roadways. Concrete roadways have joints, and wheels passing over these joints set up pressure waves which propagate up to and are detected by the sensor. The result of this is that each vehicle axle is counted several times.
A solution to this problem has been found which consists in using a long thin sensor of the piezo-electric type coated with a first layer of resin and disposed in a groove in the roadway, the walls of said groove being coated with a bonding layer and the space between the first resin and the bonding layer being filled with a second resin of a rubbery kind. This method, although effective, is tricky to apply due to the fragility of the sensor and to the multiplicity of operations to be carried out in situ.
The present invention therefore aims to provide a strong detector which is easy to manufacture in a factory, to transport and to handle and which requires only a minimum of operations in situ.